Southwest Airlines is ending its pandemic-era policy of underselling flights to allow middle seats to remain open at the end of November.

Dallas-based Southwest Airlines, which had been selling flights to only 65% capacity, said it will sell all the seats on its planes for travel starting Dec. 1, but the company will also be “pairing this change with enhanced flexibility for customers on fuller flights to rebook to another flight, if desired.”

Because Southwest doesn’t assign seats, that gave enough free seats on aircraft so that no one had to sit in the middle between strangers.

“According to research put forth within the last two weeks by several reputable institutions, all arriving at the same conclusion, the risk of breathing COVID-19 particles on an airplane is virtually non-existent, with the combination of air filtration and face covering requirements,” Southwest CEO Gary Kelly said in a statement.

The announcement came during Southwest’s third-quarter earnings release, when the carrier reported a $1.2 billion loss for the three months ending Sept. 30; revenues were down 68% from a year ago.

With Southwest's move, Delta is the only one of the four largest airlines that hasn't lifted the middle seat free policy yet. Delta said it won't sell middle seats through Jan. 6, giving enough time to space out through the holiday season. Fort Worth-based American and Chicago-based United started selling middle seats months ago.

"This practice of effectively keeping middle seats open bridged us from the early days of the pandemic, when we had little knowledge about the behavior of the virus, to now," Kelly said.

Southwest has been contacting customers since this summer when flights have been approaching capacity to offer them seats on other planes that are less full.

Airline trade groups and unions have said that planes need to be roughly 75% full for a carrier to break even in a normal price environment, which this is now.

In the last two weeks, both the Department of Defense's Transportation Command and the International Air Transport Association released studies saying that the risk of catching COVID-19 during a flight is low if passengers are wearing masks and following other safety guidelines.

IATA says only 44 cases of COVID-19 transmission have been tied directly to flying on a commercial airplane.

Airlines themselves say their air filtering systems cleans more than 99% of particles from air and cycles in new air every two to three minutes.

Even though Southwest is selling middle seats ago, there's a good chance there will still be plenty of open spots on aircraft in the near future.

Southwest’s planes were only 50% to 55% full for the month of October so far and the company expects it to remain that way in October, despite massive reductions in flying schedules to match demand.